Generally, the electronic thermometer includes a temperature sensor to sense a body temperature, and a detection signal from this temperature sensor is subjected to a signal processing, so as to display an actual measurement value. Since just after starting the measurement, there is a difference between the temperature of the sensor and the body temperature, it takes time to attain a thermal equilibrium state between the temperature sensor and a part to be measured.
Therefore, in the electronic thermometer, an equilibrium temperature in the thermal equilibrium state is predicted based on a change in the actual measurement value. The predictive value is sequentially updated and displayed, and thereby reducing the measuring time.
The prediction of the equilibrium temperature is carried out, typically, by monitoring the measured temperature and its rate of change, and calculating a prediction function using the measured temperature and the rate of change as variables. There are proposed various electronic thermometers, which predict the equilibrium temperature by utilizing this prediction function.
By way of example, in the prediction of the equilibrium temperature according to the prediction function, there is a problem that prediction accuracy is deteriorated if the prediction function that is used for the temperature prediction is not appropriate. In order to solve this problem, an electronic thermometer having the following function is proposed: More than one prediction functions are prepared to predict the equilibrium temperature, and the equilibrium temperature is predicted at specified time intervals. When a difference between a current equilibrium temperature predictive value and a previous equilibrium temperature predictive value is out of a predetermined range, a new predicted function is selected. On the other hand, if it falls in the predetermined range, the equilibrium temperature predictive value is displayed, and the predictive calculation is continued (see patent document 1).
For a prediction of the equilibrium temperature enabling a reduction of influences of individual differences on the measurement accuracy, another type of electronic thermometer having the following function is proposed: Temperature values outputted from a sensor is sampled, a parameter part of the linear TL=A−t′t is calculated by the regression method, based on a logarithmic value of time differentiation of each detection output. Here, “TL” represents the logarithmic value of the time differentiation of each detection output, “t” represents time, and both “A” and “t′” represent parameter parts. Then, the predictive calculation is performed to obtain a body temperature after attaining the thermal equilibrium state, based on the value being calculated (see patent document 2).
For predicting an equilibrium temperature without an influence of an initial temperature and a thermal time constant of the sensor, there is another electronic thermometer being proposed, having the following function: Values of three points T1, T2, and T3 in the state before the sensor and an object to be measured attain the thermal equilibrium are used, and an equilibrium temperature is predicted by Tu=T2^2−T1T3)/(2T2−T1−T3). It is to be noted here that the sign “^” represents exponentiation (see patent document 3).
Patent document 1: Japanese Examined Patent Application Publication No. 02-59418
Patent document 2: Japanese Examined Patent Application Publication No. 04-7456
Patent document 3: Japanese Unexamined Patent Application Publication No. 55-71919